When Fromm moved to Mexico City in 1950, he became a professor at the National Autonomous University[?] in Mexico and established a psychoanalytic section at the medical school there. He taught at the university until his retirement in 1965. Meanwhile, he taught as a professor of psychology at Michigan State University from 1957 to 1961 and as an adjunct professor of psychology at the graduate division of Arts and Sciences at New York University after 1962. All the while, Fromm maintained his own clinical practice and published a series of books.

Beginning with his first seminal work, Escape from Freedom, first published in 1941, Fromm's writings were notable as much for their social and political commentary as for their philosophical and pyschological underpinnings. His second seminal work, Man for Himself: An Inquiry into the Psychology of Ethics, first published in 1947, was a continuation of Escape from Freedom. Taken together, these books outlined Fromm's theory of human character, which was a natural outgrowth of Fromm's theory of human nature. Fromm's most popular book was The Art of Loving, an international bestseller first published in 1956, which recapitulated and complemented the theoretical principles of human nature found in Escape from Freedom and Man for Himself, principles which were revisited in many of Fromm's other major works.

The cornerstone of Fromm's humanistic philosophy is his interpretation of the biblical story of Adam and Eve's exile from the Garden of Eden. Drawing on his knowledge of the Talmud, Fromm pointed out that being able to distinguish between good and evil is generally considered to be a virtue, and that biblical scholars generally consider Adam and Eve to have sinned by disobeying God and eating from the Tree of Knowledge. However, departing from traditional religious orthodoxy, Fromm extolled the virtues of humans taking independent action and using reason to establish moral values rather than adhering to authoritarian moral values.

Beyond a simple condemnation of authoritarian value systems, Fromm used the story of Adam and Eve as an allegorical explanation for human biological evolution and existential angst, asserting that when Adam and Eve ate from the Tree of Knowledge, they became aware of themselves as being separate from nature while still being a part of it. This is why they felt "naked" and "ashamed": They had evolved into human beings, conscious of themselves, their own mortality, and their powerlessness before the forces of nature and society, and no longer united with the universe as they were in their instinctive[?], pre-human existence as animals. According to Fromm, the awareness of a disunited human existence is the source of all guilt and shame, and the solution to this existential dichotomy is found in the development of one's uniquely human powers of love and reason. However, Fromm so distinguished his concept of love from popular notions of love that his reference to this concept was virtually paradoxical.

Fromm considered love to be an interpersonal creative capacity rather than an emotion, and he distinguished this creative capacity from what he considered to be various forms of narcissistic neuroses and sado-masochistic tendencies that are commonly held out as proof of "true love." Indeed, Fromm viewed the experience of "falling in love" as evidence of one's failure to understand the true nature of love, which he believed always had the common elements of care, responsibility, respect, and knowledge. Drawing from his knowledge of the Talmud, Fromm pointed to the story of Jonah, who did not wish to save the residents of Nineveh from the consequences of their sin, as demonstrative of his belief that the qualities of care and responsibility are generally absent from most human relationships. Fromm also asserted that few people in modern society had respect for the autonomy of their fellow human beings, much less the objective knowledge of what other people truly wanted and needed.